In recent years, microRNAs (miRs) have emerged as an important novel class of regulatory RNA, which have a profound impact on a wide array of biological processes.
These small (typically 18-24 nucleotides long) non-coding RNA molecules can modulate protein expression patterns by promoting RNA degradation, inhibiting mRNA translation, and also affecting gene transcription. miRs play pivotal roles in diverse processes such as development and differentiation, control of cell proliferation, stress response and metabolism. The expression of many miRs was found to be altered in numerous types of human cancer, and in some cases strong evidence has been put forward in support of the conjecture that such alterations may play a causative role in tumor progression. There are currently about 1,220 known human miRs.
Classification of cancer has typically relied on the grouping of tumors based on histology, cytogenetics, immunohistochemistry, and known biological behavior. The pathologic diagnosis used to classify the tumor taken together with the stage of the cancer is then used to predict prognosis and direct therapy. However, current methods of cancer classification and staging are not completely reliable.
Lung cancer is one of the most common causes of cancer death worldwide, and non-small cell lung cancer (NSCLC) accounts for nearly 80% of those cases. Many genetic alterations associated with the development and progression of lung cancer have been reported, but the precise molecular mechanisms remain unclear.
The classification of lung tumors poses a diagnostic challenge and there is lack of standardized techniques for tumor subtyping which determines selection of treatment options. Moreover, in about 20% of cases a subclassification is not possible on preoperative specimens.
Making the correct diagnosis and specifically the distinction between primary lung cancers of squamous cell carcinoma, non-squamous NSCLC, carcinoid and small cell carcinoma has practical importance for choice of therapy. To-date there is no objective standardized test for accurate subclassification of lung cancers. Thus, there is an unmet need for a reliable method for distinguishing between specific lung cancers.